The intelligence that characterizes our species has allowed us to accomplish incredible feats never before seen in the animal world: building civilizations, using language, creating very large social networks, being aware and even being able (almost) to read the lie.
However, there are reasons to believe that having a privileged brain has cost us dearly.
The price of a big brain
From the point of view of biology, intelligence comes at a price. And it is also a price which in certain situations can be very expensive. The use of technology and the use of knowledge passed down from generations past can make us forget this, and yet, since Darwin has included us in the evolutionary tree and science is unraveling, the relationship between the brain and our behavior, the line that separates us from other animals has collapsed. Thanks to its demolition, a new problem is foreseen.
Homo sapiens, as life forms subject to natural selection, have characteristics that can be useful, unnecessary or harmful depending on the context. Intelligence, our main trait as human beings, will it not be another characteristic? Is it possible that language, memory, the ability to plan … are just strategies that have been developed in our body as a result of natural selection?
The answer to both questions is “yes”. Greater intelligence is based on drastic anatomical changes; our cognitive capacity is not a gift bestowed by the spirits, but is explained, at least in part, by drastic changes at the neuroanatomical level compared to our ancestors.
This idea, which turned out to be so expensive to admit in Darwin’s day, implies that even using our brains, a set of organs that we find so clearly beneficial in every way, can sometimes prove to be beneficial. a burden.
Of course, one could argue at length about whether the cognitive advancements we have caused more fortune or more pain. But, to get to what is simple and straightforward, the main disadvantage of having a brain like ours is, in biological terms, its very high energy consumption.
Energy consumption in the brain
Over the past million years, the evolutionary line from the extinction of our last common ancestor with chimpanzees to the emergence of our species has been characterized, among other things, by seeing how the brains of our ancestors were becoming increasingly bigger. With the advent of the genus Homo, just over 2 million years ago, this size of the brain in proportion to the body increased sharply, and since then this set of organs has grown over the millennia.
The result was that the amount of neurons, glial cells, and brain structures “freed” from the obligation to engage in routine tasks such as controlling muscles or maintaining vital signs increased dramatically. This meant that they could devote themselves to processing information already processed by other groups of neurons, causing for the first time the thought of a primate to have the “layers” of sufficient complexity to allow the emergence of abstract ideas, The use of language, the creation of long-term strategies, and ultimately everything we associate with the intellectual virtues of our species.
However, biological evolution is not something that in itself costs the price of these physical changes in our nervous system. be healthy and well-groomed.
In order to preserve a functioning brain, you need resources, that is to say energy … and it turns out that the brain is an energetically very expensive organ: although it makes up about 2% of the total body weight, it consumes more or less 20% of energy used at rest. In other contemporary monkeys with us, the size of the brain compared to the rest of the body is smaller and, of course, its consumption is too: on average, about 8% of energy at rest. The energy factor is one of the main drawbacks linked to the brain expansion necessary to achieve an intelligence similar to ours.
Who paid for brain expansion?
The energy to develop and nurture these new brains has to come from somewhere. The hardest part is knowing what changes in our body were used to pay for this brain expansion.
Until recently, one explanation for this compensation process was that of Leslie Aiello and Peter Wheeler.
The costly tissue hypothesis
seconds Aiello and Wheeler’s “expensive fabric” hypothesisThe increased demand for energy produced by a larger brain also had to be offset by a shortening of the gastrointestinal tract, another part of our body that is also very energy-intensive. The brain and gut competed for an evolutionary period for insufficient resources, so one had to develop at the expense of the other.
To maintain a more complex cerebral machinery, our bipedal ancestors could not depend on the few vegetarian mosos available in the savannah; they needed a diet that included a significant amount of meat, a food very high in protein. At the same time, stopping relying on plants for lunch has allowed the digestive system to shorten, With consequent energy savings. In addition, it is quite possible that the habit of hunting regularly was both the cause and the consequence of an improvement in general intelligence and the management of its corresponding energy consumption.
In short, according to this hypothesis, the appearance in nature of a brain like ours would be an example of a clear trade-off: the gain of one quality leads to the loss of at least one other quality. Natural selection isn’t impressed with the appearance of a brain like ours. His reaction is more, “So you have chosen to play the intelligence card … well, let’s see how you are from now on.”
However, Aiello and Wheeler’s hypothesis lost popularity over time, as the data on which it was based were unreliable. It is currently considered that there is little evidence that the increase in the brain would be offset by compensation as clear as the reduction in the size of certain organs and that much of the loss of available energy has been mitigated by brain development. . However, this change alone did not have to fully compensate for the sacrifice involved in using resources to maintain an expensive brain.
For some researchers, part of the reductions that have been made for this purpose is reflected in the decreasing strength of our ancestors and ourselves.
The weakest primate
Although an adult chimpanzee rarely exceeds 170 cm in height and 80 kg, it is well known that no member of our species could win a melee fight with these animals. The strangest of these monkeys would be able to grab average Homo sapiens by the ankle and rub the ground with it.
This is a fact mentioned, for example, in the documentary Project Nim, in which the story of a group of people who tried to raise a chimpanzee as if it were a human baby is told; In addition to the difficulties in educating the simi, there was the danger of his temper tantrums, which could lead to serious injuries with alarming ease.
This fact is not accidental and has nothing to do with this simplistic view of nature that wild beasts are characterized by their strength. It is very possible that this humiliating difference in the strength of each species it is due to the development that our brain has undergone throughout its biological evolution.
In addition, it seems that our brains have had to develop new ways of handling energy. In a research, the results were published a few years ago. years in PLoS ONE, he will verify that the metabolites used in various areas of our brain (that is to say the molecules used by our body to intervene in the extraction of energy from other substances) have evolved at a much faster rate than those of other primate species. On the other hand, in the same research it was observed that by eliminating the factor of the size difference between the species, ours has half the strength of that of other non-extinct apes that have been studied.
Increased consumption of brain energy
As we do not have the same bodily robustness as other large organisms, this increased consumption at the level of the head must be constantly compensated by intelligent means of finding energy resources using the whole body.
This is why we are on an evolutionary road with no turning back: we cannot stop looking for new ways to cope with the changing challenges of our environment if we do not want to die. paradoxically, we depend on the ability to plan and imagine provided to us by the very organ that has stolen our strengths from us.
- Aiello, LC, Wheeler, P. (1995). The facial tissue hypothesis: the brain and digestive system in human and primate evolution. Current Anthropology, 36, p. 199 – 221.
- Arsuaga, JL and Martínez, I. (1998). The chosen species: the long march of human evolution. Madrid: Ediciones Planeta.
- Bozek, K., Wei, Y., Yan, Z., Liu, X., Xiong, J., Sugimoto, M. et al. (2014). The exceptional evolutionary divergence of the brain and muscle metabolomes parallels human physical and cognitive uniqueness. Plos Biology, 12 (5), e1001871.